Pixel structure having high aperture ratio and circuit

ABSTRACT

A pixel circuit and a pixel structure having high aperture ratio are provided. A first gate electrode, a layer including a first source electrode and a first drain electrode, and an etching stopper layer, a first semiconductor layer, and a gate isolation layer sandwiched between the first gate electrode and the layer of the first source electrode and the first drain electrode construct a first thin film transistor. A second gate electrode, a layer including a second source electrode and a second drain electrode, and an etching stopper layer, a second semiconductor layer, and the gate isolation layer sandwiched between the second gate electrode and the layer of the second source electrode and the second drain electrode construct a second thin film transistor. An isolation layer with a flat top surface is sandwiched between a transparent electrode and a pixel electrode to form a transparent capacitor.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending U.S. patent applicationSer. No. 14/426,987, filed on Mar. 9, 2015, which is a national stage ofPCT Application Number PCT/CN2014/086890, filed on Sep. 19, 2014,claiming foreign priority of Chinese Patent Application Number201410443931.9, filed on Sep. 2, 2014.

FIELD OF THE INVENTION

The present invention relates to the field of display technology, andmore particularly to a pixel structure having a high aperture ratio anda circuit.

BACKGROUND OF THE INVENTION

A flat panel display possesses advantages of being ultra thin, powersaved and radiation free and has been widely utilized. Present flatpanel displays mainly comprise a LCD (Liquid Crystal Display) or an OLED(Organic Light Emitting Display).

The organic light emitting display possesses outstanding properties ofself-illumination, no required back light, high contrast, being ultrathin, wide view angle, fast response, being applicable for flexiblepanel, wide usage temperature range, simple structure and manufactureprocess and etc., and therefore, it is considered to be a new applicabletechnology for the next generation flat panel display.

The OLEDs can be categorized as PM-OLED (Passive matrix OLED) andAM-OLED (Active matrix OLED). The AM-OLED panels belong to activedisplay type, and require manufacturing pixel structures in array on thearray substrate. As shown in FIG. 1, generally in each of the pixelstructures in the present AM-OLED, two Thin Film Transistors (TFTs)sandwich a storage capacitor in-between. Specifically, the first thinfilm transistor TFT1′ comprises a first gate electrode 210, a firstsource electrode/a first drain electrode 610 and an etching stopperlayer 500, a first semiconductor layer 410, a gate isolation layer 300sandwiched in-between; the second thin film transistor TFT2′ comprises asecond gate electrode 220, a second source electrode/a second drainelectrode 620 and an etching stopper layer 500, a second semiconductorlayer 420, a gate isolation layer 300 sandwiched in-between; the storagecapacitor C′ comprises a first metal electrode 230 formed by the firstand the second gate electrodes 210, 220, and a second metal electrode630 formed by the first source electrode/the first drain electrode, thesecond source electrode/the second drain electrode 610, 620, and theetching stopper layer 500 and the gate isolation layer 300 sandwichedbetween the two electrodes. Because the metal material shields the lightand blocks the penetration of the light, the first and the second thinfilm transistors TFT1′, TFT2′ and the storage capacitor C′ must occupy acertain area of the pixel, which leads to a reduced activation area ofthe pixel, meaning an aperture ratio is reduced. It enormously restrictsthe usage ratio of the light. Particularly as for the high resolution,bottom emitting AM-OLED, the decrease of the aperture ratio gets evenworse, which easily causes problems of the insufficient brightness andover large power consumption.

FIG. 2 is an equivalent circuit diagram of FIG. 1. The first thin filmtransistor TFT1′ is employed as a single switch thin film transistor.The second thin film transistor TFT2′ is employed as a drive thin filmtransistor. Specifically, a gate electrode of the first thin filmtransistor TFT1′ is coupled to a gate drive voltage signal V_(gate), anda source electrode thereof is coupled to a data drive voltage signalV_(data), and a drain electrode thereof is coupled to a gate electrodeof the second thin film transistor TFT2′; a source electrode of thesecond thin film transistor TFT2′ is coupled to a drive voltage signalV_(dd), and a drain electrode thereof is coupled to an anode of theorganic light emitting diode D; a cathode of the organic light emittingdiode D is coupled to a ground signal V_(ss); one electrode of thestorage capacitor C′ is coupled to the gate electrode of the second thinfilm transistor TFT2′, and the other electrode thereof is coupled to thesource electrode of the second thin film transistor TFT2′.

The working principle of the circuit is as follows. When the gate drivevoltage signal V_(gate) is present, the first thin film transistor TFT1′is conducted, and the data drive voltage signal V_(data) is inputted tothe gate electrode of the second thin film transistor TFT2′ and thesecond thin film transistor TFT2′ is conducted. The drive voltagesignal, V_(dd), drives the organic light emitting diode D to displayafter being amplified by the second thin film transistor TFT2′. When thegate drive voltage signal V_(gate) disappears, the storage capacitor C′is a major means to maintain the voltage level of the pixel electrode.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a pixel structurehaving high aperture ratio, capable of increasing the activation area ofthe pixel and raising the aperture ratio to increase the displaybrightness and reduce the power consumption.

Another objective of the present invention is to provide a circuit of apixel structure having high aperture ratio, beneficial to raise theaperture ratio and promote the display effect.

For realizing the aforesaid objective, the present invention firstprovides a pixel structure having high aperture ratio, comprising asubstrate, a first gate electrode and a second gate electrode, locatedabove one region of the substrate; a gate isolation layer, located onthe first gate electrode, the second gate electrode and the substrate,such that the gate isolation layer completely covers the first gateelectrode, substantially covers the substrate, and exposes two ends ofthe second gate electrode; a first semiconductor layer, located on thegate isolation layer and right over the first gate electrode; a secondsemiconductor layer, located on the gate isolation layer and right overthe second gate electrode; an etching stopper layer, located on thefirst semiconductor layer, the second semiconductor layer and the gateisolation layer; a first source electrode and a first drain electrode,located on the first semiconductor layer and the etching stopper layer;a second source electrode and a second drain electrode, located on thesecond semiconductor layer and the etching stopper layer, such that thefirst source electrode and first drain electrode are connected to thefirst semiconductor layer and one of the first source electrode and thefirst drain electrode is connected to one of the exposed ends of thesecond gate electrode, and the second source electrode and the seconddrain are connected to the second semiconductor layer; a protectivelayer, located on the first source electrode, the first drain electrode,the second source electrode, the second drain electrode and the etchingstopper layer; a transparent electrode, located on the protective layerand above another region of the substrate, such that the transparentelectrode is connected to the other one of the exposed ends of thesecond gate electrode; an isolation layer with a flat top surface,located on the protective layer and the transparent electrode; a pixelelectrode, located on the isolation layer with the flat top surface,such that the pixel electrode is connected to one of the second sourceelectrode and the second drain electrode and overlaps with thetransparent electrode; a pixel definition layer, located on theisolation layer with the flat top surface and the pixel electrode, suchthat the pixel definition layer comprises an opening corresponding to anoverlapping district of the pixel electrode and the transparentelectrode; wherein the first gate electrode, a layer of the first sourceelectrode and the first drain electrode, and the etching stopper layer,the first semiconductor layer, and the gate isolation layer sandwichedbetween the first gate electrode and the layer of the first sourceelectrode and the first drain electrode construct a first thin filmtransistor; the second gate, a layer of the second source electrode andthe second drain electrode, and the etching stopper layer, the secondsemiconductor layer, and the gate isolation layer sandwiched between thesecond gate electrode and the layer of the second source electrode andthe second drain electrode construct a second thin film transistor; andthe isolation layer with a flat top surface is sandwiched between thetransparent electrode and the pixel electrode to form a transparentcapacitor.

The transparent capacitor constructs an activation area part of thepixel structure.

The transparent electrode is an indium tin oxide (ITO) transparentelectrode or an indium zinc oxide (IZO) transparent electrode, and thepixel electrode is an ITO pixel electrode or an IZO pixel electrode.

The pixel structure having high aperture ratio further comprises aphotoresist spacer located on the pixel definition layer.

The pixel structure having high aperture ratio further comprises a firsttop gate electrode right over the first gate electrode and between theprotective layer and the isolation layer with the flat top surface, anda second top gate electrode right over the second gate electrode andbetween the protective layer and the isolation layer with the flat topsurface.

The first and second top gate electrodes and the transparent electrodeare formed at the same time.

The first semiconductor layer is an indium gallium zinc oxide (IGZO)semiconductor layer, and the second semiconductor layer is an IGZOsemiconductor layer.

The present invention further provides a circuit of a pixel structurehaving high aperture ratio, comprising a first thin film transistor, asecond thin film transistor, a transparent capacitor, and an organiclight emitting diode, wherein the transparent capacitor comprises twoelectrodes that are both transparent electrodes; the first thin filmtransistor comprises a gate electrode that is coupled to a gate drivevoltage signal, a source electrode that is coupled to a data drivevoltage signal, and a drain electrode coupled to a gate electrode of thesecond thin film transistor; a source electrode of the second thin filmtransistor is coupled to a drive voltage signal, and a drain of thesecond thin film transistor is coupled to an anode of the organic lightemitting diode; a cathode of the organic light emitting diode is coupledto a ground signal; and one of the two electrodes of the transparentcapacitor is coupled to the gate electrode of the second thin filmtransistor, and the other one of the two electrodes of the transparentcapacitor is coupled to one of the source electrode and the drainelectrode of the second thin film transistor.

The circuit of the pixel structure having high aperture ratio furthercomprises an opaque capacitor, and one electrode of the opaque capacitoris coupled to the gate electrode of the second thin film transistor, andthe other electrode of the opaque capacitor is coupled to one of thesource electrode and the drain electrode of the second thin filmtransistor.

The source electrode and the drain electrode of the first thin filmtransistor are switchable, and the source electrode and the drainelectrode of the second thin film transistor are also switchable.

The benefits of the present invention are: according to the pixelstructure having high aperture ratio of the present invention, byarranging the transparent capacitor constructed by the transparentelectrode and the pixel electrode, and the transparent capacitor isemployed as the activation area part for increasing the activation areaof the pixel and raising the aperture ratio to increase the displaybrightness and reduce the power consumption. According to the circuit ofthe pixel structure having high aperture ratio provided by the presentinvention, the aperture ratio can be raised and the display effect canbe promoted by arranging the transparent capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

The technical solution, as well as beneficial advantages, of the presentinvention will be apparent from the following detailed description of anembodiment of the present invention, with reference to the attacheddrawings.

In drawings,

FIG. 1 is a sectional diagram of a pixel structure according to priorart;

FIG. 2 is an equivalent circuit diagram of the pixel structure shown inFIG. 1;

FIG. 3 is a sectional diagram of a pixel structure having high apertureratio according to the first embodiment of the present invention;

FIG. 4 is a sectional diagram of a pixel structure having high apertureratio according to the second embodiment of the present invention;

FIG. 5 is a schematic diagram of a circuit of a pixel structure havinghigh aperture ratio according to the first embodiment of the presentinvention;

FIG. 6 is a schematic diagram of a circuit of a pixel structure havinghigh aperture ratio according to the second embodiment of the presentinvention; and

FIG. 7 is a schematic diagram of a circuit of a pixel structure havinghigh aperture ratio according to the third embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In order to better understand the characteristics and technical aspectof the invention, reference is made to the following detaileddescription of the present invention in association with the drawings.

The present invention first provides a pixel structure having highaperture ratio and FIG. 3 shows a first embodiment thereof. The pixelstructure having a high aperture ratio comprises a substrate 1, whereinthe substrate 1 can be a glass substrate or a plastic substrate;

a first gate electrode 21 and a second gate electrode 22, located aboveone region of the substrate 1 and on the substrate 1, wherein the firstgate electrode 21 and the second gate electrode 22 are formed with thesame first metal film layer which has been patterned;

a gate isolation layer 3 located on the first gate electrode 21, thesecond gate electrode 22 and the substrate 1 such that the gateisolation layer 3 completely covers the first gate electrode 21,substantially covers the substrate 1, and exposes two ends of the secondgate electrode 22;

a first semiconductor layer 41, located on the gate isolation layer 3and right over the first gate electrode 21; a second semiconductor layer42, located on the gate isolation layer 3 and right over the second gateelectrode 22; wherein the first semiconductor layer 41 and the secondsemiconductor layer 42 are formed with the same semiconductor layerwhich has been patterned;

an etching stopper layer 5, located on the first semiconductor layer 41,the second semiconductor layer 42 and the gate isolation layer 3;

a first source electrode and a first drain electrode 61, located on thefirst semiconductor layer 41 and the etching stopper layer 5; a secondsource electrode and a second drain electrode 62, located on the secondsemiconductor layer 42 and the etching stopper layer 5 wherein the firstsource electrode and the first drain electrode 61 and the second sourceelectrode and the second drain electrode 62 are formed with the samesecond metal film layer which has been patterned; and the first sourceelectrode and the first drain electrode 61 are connected to the firstsemiconductor layer 41 and one of the first source electrode and thefirst drain electrode is connected to one of the two exposed ends of thesecond gate 22, and the second source electrode and the second drainelectrode 62 are connected to the second semiconductor layer 42;

a protective layer 7, located on the first source electrode, the firstdrain electrode, the second source electrode, the second drain electrodeand the etching stopper layer 5;

a transparent electrode 8, located on the protective layer 7 and aboveanother region of the substrate 1, such that the transparent electrode 8is connected to the other one of the two exposed ends of the second gate22;

an isolation layer 9 having a flat top surface, located on theprotective layer 7 and the transparent electrode 8;

a pixel electrode 10, located on the isolation layer 9, such that thepixel electrode 10 is connected to one of the second source electrodeand the second drain electrode 62 and overlaps with the transparentelectrode 8;

a pixel definition layer 11, located on the isolation layer 9 and thepixel electrode 10, such that the pixel definition layer 11 comprises anopening corresponding to an overlapping district of the pixel electrode10 and the transparent electrode 8; and

a photoresist spacer 12 located on the pixel definition layer 11.

The first gate 21, the layer of the first source electrode and the firstdrain electrode 61, with the etching stopper layer 5, the firstsemiconductor layer 41, and the gate isolation layer 3 sandwichedbetween the first gate electrode and the layer of the first sourceelectrode and the first drain electrode construct a first thin filmtransistor TFT1; the second gate 22, the layer of the second sourceelectrode and the second drain electrode 62, with the etching stopperlayer 5, the second semiconductor layer 42, and the gate isolation layer3 sandwiched between the second gate electrode and the layer of thesecond source electrode and the second drain electrode construct asecond thin film transistor TFT2; and the isolation layer 9 having aflat top surface is sandwiched between the transparent electrode 8 andthe pixel electrode 10 to form a transparent capacitor C.

Specifically, the first semiconductor layer 41 is an indium gallium zincoxide (IGZO) semiconductor layer, and the second semiconductor layer 42is an IGZO semiconductor layer.

The transparent electrode 8 is an indium tin oxide (ITO) transparentelectrode or an indium zinc oxide (IZO) transparent electrode and thetransparent electrode 8 can be manufactured to have various shapes; thepixel electrode 10 is an ITO pixel electrode or an IZO pixel electrode.

Both the transparent electrode 8 and the pixel electrode 10 aretransparent which light can pass through. The transparent capacitor Cconstructs the activation area part of the pixel structure and iscapable of increasing the activation area of the pixel and raising theaperture ratio to increase the display brightness and reduce the powerconsumption.

Significantly, the transparent capacitor C may completely replace opaquecapacitors constructed by two metal electrodes according to the priorart, or partially replacing the opaque capacitors, both helping increasethe activation area of the pixels and raising the aperture ratio.

Referring to FIG. 4, which is the second embodiment of the pixelstructure having high aperture according to the present invention, thedifferences of the second embodiment from the first embodiment are thatthe pixel structure having high aperture ratio further comprises a firsttop gate electrode 81 right over the first gate electrode 21 and betweenthe protective layer 7 and the isolation layer 9, and a second top gateelectrode 82 right over the second gate electrode 22 and between theprotective layer 7 and the isolation layer 9. Correspondingly, both thefirst thin film transistor TFT1 and the second thin film transistor TFT2comprise a double gate structure. For making the most of the manufactureprocess and raising the production efficiency, the first and second topgate electrodes 81, 82 and the transparent electrode 8 are formed in thesame manufacture process at the same time. The material of the first andsecond top gate electrodes 81, 82 and the material of the transparentelectrode 8 are the same, which is ITO or IZO. Other materials are thesame as the first embodiment. A repeated description is omitted here.

The present invention further provides a circuit of a pixel structurehaving high aperture ratio. FIG. 5 shows the first embodiment of thecircuit, comprising a first thin film transistor TFT1, a second thinfilm transistor TFT2, a transparent capacitor C, and an organic lightemitting diode D. Two electrodes of the transparent capacitor C are bothtransparent electrodes.

The first thin film transistor TFT1 comprises a gate electrode that iscoupled to a gate drive voltage signal V_(gate), a source electrode thatis coupled to a data drive voltage signal V_(data), and a drainelectrode that is coupled to a gate electrode of the second thin filmtransistor TFT2; a source electrode of the second thin film transistorTFT2 is coupled to a drive voltage signal V_(dd), and a drain electrodeof the second thin film transistor is coupled to an anode of the organiclight emitting diode D; a cathode of the organic light emitting diode Dis coupled to a ground signal V_(ss); one of the two electrodes of thetransparent capacitor C is coupled to the gate electrode of the secondthin film transistor TFT2, and the other one of the two electrodes iscoupled to the source electrode of the second thin film transistor TFT2.

The first thin film transistor TFT1 is employed as a signal switch thinfilm transistor, and the second thin film transistor TFT2 is employed asa drive thin film transistor. The working principle of the circuit is asfollows. When the gate drive voltage signal V_(gate) is present, thefirst thin film transistor TFT1 is conducted, and the data drive voltagesignal V_(data) is inputted to the gate electrode of the second thinfilm transistor TFT2 and the second thin film transistor TFT2 isconducted. The drive voltage signal, V_(dd), drives the organic lightemitting diode D to display after being amplified by the second thinfilm transistor TFT2. When the gate drive voltage signal V_(gate)disappears, the transparent capacitor C is employed to maintain thevoltage level of the pixel electrode.

The aperture ratio can be raised and the display effect can be promotedbecause the transparent capacitor C is arranged in the circuit.

Referring to FIG. 6, which shows a second embodiment of the circuit ofthe pixel structure having high aperture according to the presentinvention, the differences of the second embodiment from the firstembodiment are that one of the two electrodes of the transparentcapacitor C is coupled to the gate electrode of the second thin filmtransistor TFT2, and the other one of the two electrodes is coupled tothe drain electrode of the second thin film transistor TFT2. The otherparts are configured to be the same as those of the first embodiment. Arepeated description is omitted here.

Referring to FIG. 7, which shows a third embodiment of the circuit ofthe pixel structure having high aperture according to the presentinvention, the differences of the third embodiment from the firstembodiment are that one of the two electrodes of the transparentcapacitor C is coupled to the gate electrode of the second thin filmtransistor TFT2, and the other one of the two electrodes is coupled tothe drain electrode of the second thin film transistor TFT2, and anopaque capacitor C″ is further included, wherein one electrode of theopaque capacitor C″ is coupled to the gate electrode of the second thinfilm transistor TFT2, and the other electrode of the opaque capacitor iscoupled to the source electrode of the second thin film transistor TFT2.

The source electrode and the drain electrode of the first thin filmtransistor TFT1 are switchable, and the source electrode and the drainelectrode of the second thin film transistor TFT2 are switchable, too.Therefore, in the third embodiment, the one electrode of the transparentcapacitor C can be coupled to the gate electrode of the second thin filmtransistor TFT2, and the other electrode of the transparent capacitor iscoupled to the source electrode of the second thin film transistor TFT2,and the one electrode of the opaque capacitor C″ can be coupled to thegate electrode of the second thin film transistor TFT2, and the otherelectrode of the opaque capacitor can be coupled to the drain electrodeof the second thin film transistor TFT2. The other parts are configuredto be the same as those of the first embodiment. A repeated descriptionis omitted here.

In conclusion, according to the pixel structure having high apertureratio of the present invention, by arranging the transparent capacitorconstructed by the transparent electrode and the pixel electrode, andthe transparent capacitor is employed as the activation area part forincreasing the activation area of the pixel and raising the apertureratio to increase the display brightness and reduce the powerconsumption. According to the circuit of the pixel structure having highaperture ratio provided by the present invention, the aperture ratio canbe raised and the display effect can be promoted by arranging thetransparent capacitor.

Above are only specific embodiments of the present invention, the scopeof the present invention is not limited to this, and to any persons whoare skilled in the art, change or replacement which is easily derivedshould be covered by the protected scope of the invention. Thus, theprotected scope of the invention should go by the subject claims.

What is claimed is:
 1. A pixel circuit, comprising a first thin filmtransistor, a second thin film transistor, a transparent capacitor, andan organic light emitting diode, which are arranged on a substrate,wherein the transparent capacitor comprises two electrodes that are bothtransparent electrodes between which an isolation layer is sandwiched;the first thin film transistor comprises a gate electrode that isadapted to receive a gate drive voltage signal, a source electrode thatis adapted to receive a data drive voltage signal, and a drain electrodecoupled to a gate electrode of the second thin film transistor; a sourceelectrode of the second thin film transistor is adapted to receive adrive voltage signal, and a drain of the second thin film transistor iscoupled to an anode of the organic light emitting diode; a cathode ofthe organic light emitting diode is grounded; and a first one of the twoelectrodes of the transparent capacitor is coupled to the gate electrodeof the second thin film transistor, and a second one of the twoelectrodes of the transparent capacitor is coupled to one of the sourceelectrode and the drain electrode of the second thin film transistor;and wherein a pixel definition layer is provided on and covering thefirst thin film transistor, the second thin film transistor, and aportion of the transparent capacitor, wherein an open area is formed inand extending through the pixel definition layer such that a most partof the transparent capacitor corresponds in position to and locatedunder the open area of the pixel definition layer and at least a portionof the second one of the two electrodes of the transparent capacitor isexposed through the open area and the first one of the two electrodes ofthe transparent capacitor is located under and covered by the isolationlayer; further comprising an opaque capacitor, wherein one electrode ofthe opaque capacitor is coupled to the gate electrode of the second thinfilm transistor, and the other electrode of the opaque capacitor iscoupled to another one of the source electrode and the drain electrodeof the second thin film transistor.
 2. The circuit of the pixelstructure as claimed in claim 1, wherein the source electrode and thedrain electrode of the first thin film transistor are switchable, andthe source electrode and the drain electrode of the second thin filmtransistor are switchable.
 3. A pixel circuit, comprising a first thinfilm transistor, a second thin film transistor, a transparent capacitor,an opaque capacitor, and an organic light emitting diode, wherein thetransparent capacitor comprises two electrodes that are both transparentelectrodes between which an isolation layer is sandwiched; the firstthin film transistor comprises a gate electrode that is adapted to agate drive voltage signal, a source electrode that is adapted to receivea data drive voltage signal, and a drain electrode coupled to a gateelectrode of the second thin film transistor; a source electrode of thesecond thin film transistor is adapted to receive a drive voltagesignal, and a drain of the second thin film transistor is coupled to ananode of the organic light emitting diode; a cathode of the organiclight emitting diode is grounded; and one of the two electrodes of thetransparent capacitor is coupled to the gate electrode of the secondthin film transistor, and the other one of the two electrodes of thetransparent capacitor is coupled to a first one of the source electrodeand the drain electrode of the second thin film transistor; oneelectrode of the opaque capacitor is coupled to the gate electrode ofthe second thin film transistor, and the other electrode of the opaquecapacitor is coupled to a second one of the source electrode and thedrain electrode of the second thin film transistor, the second one ofthe source electrode and the drain electrode of the second thin filmtransistor being different from the first one of the source electrodeand the drain electrode of the second thin film transistor; and whereina pixel definition layer is provided on and covering the first thin filmtransistor, the second thin film transistor, and a part of thetransparent capacitor, wherein an open area is formed in and extendingthrough the pixel definition layer such that a portion of thetransparent capacitor corresponds in position to and located under theopen area of the pixel definition layer and the second one of the twoelectrodes of the transparent capacitor is exposed through the open areaand the first one of the two electrodes of the transparent capacitor islocated under and covered by the isolation layer and connected to thegate electrode of the second thin film transistor.
 4. The circuit of thepixel structure as claimed in claim 3, wherein the first one of thesource electrode and the drain electrode of the second thin filmtransistor is the drain electrode, and the second one of the sourceelectrode and the drain electrode of the second thin film transistor isthe source electrode.